1. Field of the Invention
The present invention relates to a magnetic read/write system that uses a fixed MR head to read magnetically recorded data from a magnetic recording medium, and to such a magnetic recording medium. More particularly, the present invention relates to a magnetic read/write system that employs a fixed MR head to read magnetically recorded data from a magnetic recording medium, with improved running durability, adherence to a head, and wear resistance and to such a magnetic recording medium.
2. Description of the Related Art
As the recording density of magnetic recording media increases, friction between a magnetic layer and components of a reading device during running has posed a significant problem and there is an increasing need to improve running durability, adherence to a head, and wear resistance of such recording media.
To meet such needs, techniques have been developed where a fatty acid ester is added to a magnetic layer of a magnetic recording medium that is mainly composed of ferromagnetic powder and binder resin (Japanese Patent Laid-Open Publication No. Sho 50-22603, Japanese Patent Laid-Open Publication No. Sho 50-153905, Japanese Patent Laid-Open Publication No. Sho 53-149302, Japanese Pent Laid-Open Publication No. Sho 55-139637, Japanese Patent Publication No. Sho 39-28367, Japanese Patent Publication No. Sho 41-18065, and Japanese Patent Publication No. Sho 47-12950).
These techniques, however, suffer a problem that many of the ester compounds that have straight-chain alkyls, which bring about their relatively high lubricating performance, have high melting points and thus form deposits on the surface of the magnetic layer at low temperatures. To cope with this, some techniques employ a fatty acid ester having a saturated or unsaturated branched hydrocarbon group with high molecular weight as an additive to the magnetic layer (Japanese Patent Publication No. Sho 47-12950, Japanese Patent Laid-Open Publication No. Sho 58-218038, Japanese Patent Laid-Open Publication No. Sho 60-205827, Japanese Patent Laid-Open Publication No. Sho 61-294637, and Japanese Patent Laid-Open Publication No. Sho 62-125529). One technique involves adding to the magnetic layer a fatty acid ester having the following general formula: 
where R11 is a straight-chain saturated alkyl having 6 to 12 carbons, R12 is a straight-chain saturated alkyl having 4 to 10 carbons, and R is a straight-chain or branched alkyl having 4 to 22 carbons (Japanese Patent No. 2559259).
One type of magnetic read/write system, which has recently been put to practical use and is intended for use in a computer back-up system, reads data stored in a magnetic recording medium using a fixed MR head that operates at a relative speed of 2.0 to 5.0 m/s with respect to the recording medium. The system, known as the linear tape drive system, operates on the basis of linear scanning, in which a magnetic tape (which may be referred to simply as a tape, hereinafter) is moved along its length with respect to the fixed MR head as the data is read along that direction. Unlike a helical scanning system, which employs a rotary head, the magnetic tape is moved at high speeds in this system. As a result, the tape is vigorously rubbed against the head or guide rolls, causing the magnetic coating to come off the tape. For this reason, the role of the lubricant has become ever more significant to minimize damage to the coating, and should the coating come off the tape, it is desirable that the coating does not stick to the surrounding area of the head gap.
No conventional fatty acid ester has ever achieved satisfactory performance when added to the magnetic layer in such a system. For example, fatty acid esters that have a saturated or unsaturated branched hydrocarbon with high molecular weight are less than satisfactory in terms of film strength and lubricating performance of the magnetic layer under low temperature conditions.
Fatty acid esters used in a magnetic disk as described in Japanese Patent No. 2559259 are less likely to crystallize and remain in a liquid state at relatively low temperatures, exhibiting lubricating property. These fatty acid esters do not readily evaporate from the surface of the magnetic layer at high temperatures, nor do they form deposits at low temperatures since fatty acid units and alcohol units present in the molecule have a limited number of carbons. Thus, the fatty acid esters are capable of providing high running durability under various conditions. However, the lubricating performance of these fatty acid esters is not sufficient because of their high dynamic viscosity. Therefore, a high friction results when the fatty acid esters are applied to the tape. This causes abrasion of the coating.
The present invention addresses the above-identified problems associated with the prior art.
Accordingly, it is an objective of the present invention to provide a magnetic read/write system that uses a fixed MR head to read magnetically recorded data from a magnetic recording medium that has improved adherence to a head, running durability and wear resistance under low temperature conditions, as well as at room temperature, and to provide such a magnetic recording medium. In particular, the present invention aims at provision of a magnetic read/write system that uses a magnetic tape exhibiting improved performances in terms of the above-described adherence, running durability, and wear resistance when used in a linear tape drive system, in which the fixed MR head reads magnetically recorded data from a magnetic recording medium formed as a tape (i.e., a magnetic tape), such as DLT4, while operating at a relative speed of 2.0 to 5.0 m/s with respect to the recording medium. It is also an objective of the present invention to provide such a magnetic tape.
In the course of their studies to find a solution to the above-described problems, the present inventors have found that the above-described objectives can be achieved by providing a non-magnetic layer that contains a specific fatty acid ester and a fatty acid between a non-magnetic support and the above-described magnetic layer and ultimately completed the present invention.
In one aspect, the present invention provides a magnetic read/write system, in which a fixed MR head serves to read magnetically recorded data from a magnetic recording medium as it operates at a relative speed of 2.0 to 5.0 m/s with respect to the magnetic recording medium comprising a non-magnetic support and a magnetic layer, wherein a fatty acid ester represented by general formula (I): 
where R1 is a hydrocarbon having 4 or less carbons, and R2 is a straight-chain hydrocarbon having 12 or more carbons, exists between a read element of the MR head and the magnetic layer.
In another aspect, the present invention provides such a magnetic recording medium comprising:
a non-magnetic support;
a magnetic layer containing a ferromagnetic powder and a binder resin, the magnetic layer formed over the non-magnetic support and having a dry thickness of 0.5 xcexcm; and
a non-magnetic layer containing a non-magnetic powder and a binder resin, the non-magnetic layer interposed between the non-magnetic support and the magnetic layer, the non-magnetic layer containing as a lubricant a fatty acid ester represented by general formula (I): 
where R1 is a hydrocarbon having 4 or less carbons, and R2 is a straight-chain hydrocarbon having 12 or more carbons, and a fatty acid having 12 or more carbons.
The fatty acid ester of the general formula (I) for use with the present invention, which is derived from fatty acids having a hydrocarbon branch at 2xe2x80x2-position, has a low solidification point and does not suffer a significant decrease in the lubricity in low temperature conditions. In addition, this fatty acid ester has a shorter fatty acid side chain as compared to the conventional fatty acid esters as represented by the general formula (II) and thus exhibits low dynamic viscosity and shear viscosity even in low temperature conditions. Accordingly, by using the fatty acid ester, not only can the friction and the wear in the tape be reduced in a wide temperature range, but also the durability under various environments is improved. Furthermore, in terms of physical properties, the fatty acid ester exhibits less oiliness, the property being characteristic of fatty acid esters. This is believed to contribute to the improvements in the adherence to a head and stickiness of the tape. In the present invention, the fatty acid ester of the general formula (I) is added only to the non-magnetic layer and is allowed to gradually migrate from the non-magnetic layer through the magnetic layer to the surface thereof. In this manner, high durability and wear-resistance can be achieved even when the tape is moved at a relative speed of 2.0 to 5.0 m/s with respect to the fixed MR head. These effects are not obtained if the fatty acid ester is added only to the magnetic layer. The concurrent presence of the fatty acid with the non-magnetic powder in the non-magnetic layer makes it possible for the fatty acid ester to migrate in the manner described above.